This invention relates to personal dosimeters in general and more particularly to an improved personal dosimeter which is of extremely simple design and which can be produced at low cost.
Over the recent years, there has been increasing concern regarding the exposure of workers to harmful substances. This has resulted in the enactment of various laws at the Federal and State levels relating to occupational health and safety. As a result, requirements are placed on facilities where harmful substances are present to monitor the exposure of their workers to these substances.
One of the typical manners of determining the presence of harmful substances has been to use a pump to draw a sample of the ambient air containing the toxic substance through a material which will absorb or adsorb the toxic substance and then extract the toxic substance therefrom and measure its concentration using a chromatograph or the like. For example, to detect the time weighted average of hydrocarbons, a tube filled with carbon has been used as a collecting medium. A pump draws the sample through the carbon where the toxic substance to be measured is trapped. Later, the toxic substance is dissolved out of the carbon and injected into a chromatograph and read in PPM. This is an expensive method, particularly because of the high cost of pumps. Further information concerning the sampling and analysis is found in an article entitled, "A Convenient Optimized Method For The Analysis Of Selected Solvent Vapors In the Industrial Atmosphere" by White et al. published in The American Industrial Hygiene Association Journal, vol. 31, March-April, 1970.
Because of the difficulties and high costs of using the aforementioned method of sampling, there have been attempts to develop a personal dosimeter. Such is disclosed, for example, in U.S. Pat. No. 3,985,017. The dosimeter disclosed therein, which is termed a Gaseous Contaminant Personal Dosimeter comprises a container, an inert porous thin barrier element forming one side of the container with the barrier element adapted to permit diffusion of the gaseous contaminants that are to be determined into the interior of the containers and a gaseous contaminant collecting medium within the container and positioned opposite the barrier element to collect the gaseous contaminant diffused from the ambient atomsphere through the barrier element. It also includes means to inhibit convection movement of the diffused gases within the container and permits the determination of gaseous contaminants in proportion to ambient concentrations independent of ambient convection patterns. Although shown as a cylindrical device in the patent, the actual device, which is sold under the trade name Gasbadge by the Walton division of Abcor, Inc. of Wilmington, Mass., is in a rectangular shape, quite similar to the shape of conventional radiation dosimeters. The dosimeter actually being produced includes a back containing a spring clip into which the collecting medium is placed, an open grid placed thereover to define diffusion geometry, a draft shield made from non-reactive porous material, a badge front with an opening to allow diffusion of gas vapors into the device and a removable protective cover. Obviously, this is a relatively expensive device, even though it is possible to replace the collection material therein.
One serious problem with the dosimeter of the aforementioned U.S. Patent is that the analysis of results are preferably carried out in a laboratory. Because of the fact that, in essence, the materials which are used to adsorb, absorb or react must be solids, it is necessary to go through a chemical analysis which is comparatively complex in order to obtain the necessary information concerning concentrations of the toxic gas in the ambient air.
There exist in the art, many collection solutions or reagents which change color depending on the concentration of a toxic substance in the solution. Quite often, the solution is a water based solution and large fields of analysis have been built around water analysis and resulting color changes with absorption. In some cases, a water sample is taken and the proper reagent added to the water. The reagent results in color depending on the concentration of the substance therein and a color comparator is then used to determine the concentration, i.e., the actual color is compared with colors relating to predetermined known concentrations. Alternatively, color measurements can be done using other types of colorimeters such as a color photometer.
In line with this, it has been common to take a collection solution and place it in an impinger. The ambient air to be measured is then drawn through the impinger by a pump with the substance under consideration absorbed into the solution which then changes color as a result. After the sample has been collected, some of the solution is poured into a cuvette and placed in an axial reader to determine the closest color match with the comparator index number. Alternatively, the color comparison can be done on a color photometer.
This gives immediate results without complicated chemical analysis. However, it does depend on the availability of a collecting solution. Attempts to use a solution in a personal dosimeter heretofore have not been successful because the solution tended to dry before the measurement time period, which might be eight hours or more, was up.
Thus, there is a need for an improved dosimeter which can use solutions, particularly solutions which indicate concentrations by color changes, to measure the amount of harmful substances, e.g., toxic gases, in the ambient air.